基于质子束辐照产生空位缺陷的石墨烯磁性调控研究

Due to its long spin-relaxation time, large spin-diffusion length and highly tunable band structure Graphene is one of the most promising materials in spintronics devices. Ideal graphene is diamagnetic and introduction of ferromagnetism via defects could significantly improve its performance in spin injection and spin-polarized current generation. Theoretical study have revealed that the vacancy defects could induce local magnetic moment and stable ferromagnetic ordering of the magnetic moment can be achieved at room temperature when the concentration of defects is in the order of 1%, which has not been experimental realized. And the mechanism responsible for the formation of defect magnetic moment and the ferromagnetic ordering remains controversial. This proposal adopts high flux proton beam to generate vacancies with high concentration and perform experimental characterization on the geometry, electronic structure and magnetism property to reveal the formation mechanism of local magnetic moment of vacancy. Meanwhile the previous predicted room temperature ferromagnetism of graphene with vacancies. And the graphene samples with various the band structure and concentration of carriers would be synthesized by gradually increasing the vacancy concentration. Based on the magnetism property of samples and first-principles calculation, the research would shed some light on the debatable origin of the ferromagnetism (Stoner ferromagnetism/Heisenberg ferromagnetism) of graphene with vacancies.

石墨烯基材料由于具有较长的自旋弛豫时间、较大的自旋扩散距离和高度可调的能带结构，在自旋电子学器件具有巨大的潜在应用价值。理想石墨烯为抗磁性材料，通过结构缺陷引入铁磁性可以显著提升石墨烯在自旋注入、自旋流产生等方面的性能。理论研究显示，石墨烯中空位缺陷可以产生局域磁矩，且当缺陷浓度达到1%量级时，磁矩可在室温下稳定的铁磁排布，但是目前尚未在实验中实现此浓度的缺陷。另外，目前的研究在缺陷磁矩的产生机制、铁磁耦合机制等方面还存在较大的争议。本项研究拟采用强流质子束辐照石墨烯产生高浓度空位缺陷，实现对空位缺陷的几何构型和电子结构的实验表征，结合磁性测量揭示缺陷磁矩的产生机制，并验证理论预言的石墨烯空位铁磁性；同时通过逐步改变缺陷浓度调制石墨烯的能级结构和载流子浓度，根据样品的磁性变化，结合第一性原理计算研究，为石墨烯空位缺陷铁磁性起源的争议（Stoner铁磁/Heisenberg铁磁）提供参考。

石墨烯基材料由于具有较长的自旋弛豫时间、较大的自旋扩散距离和高度可调的能带结构，在自旋电子学器件具有巨大的潜在应用价值。理想石墨烯为抗磁性材料，通过结构缺陷引入铁磁性可以显著提升石墨烯在自旋注入、自旋流产生等方面的性能。本项目研究了基于晶格缺陷和离子/分子吸附的石墨烯、单层MoS2等二维材料的磁性调控。我们通过质子束辐照在液相剥离制备的高质量石墨烯上引入晶格缺陷来产生局域磁矩和费米面处缺陷能级，实现石墨烯的磁性调控。我们详细研究了质子束辐照条件（流强、质子动能等）与缺陷类型、密度和电子结构的关系，为磁性缺陷（空位和zigzag边缘）的可控制备提供参考。我们还研究了通过引入S空位、Li离子和BV分子吸附实现对过渡金属掺杂单层MoS2的磁性调控。我们利用等离子体辐照在V掺杂单层MoS2中引入S空位缺陷，缺陷能级通过与V 3d能级杂化而发生自旋极化，由BMP机制形成铁磁耦合。在过渡金属掺杂单层MoS2上吸附Li离子和BV分子则可以通过电荷转移增强过渡金属局域的局域磁矩，实现铁磁性调控。另外，我们通过在Co掺杂单层MoS2上进行Cr离子修饰，实现了铁磁性和高PL性能在MoS2中共存，可用于自旋光子学器件。